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I'm in the middle of installing a Trane 3 ton heat pump sytem. There are 15 6 inch supplies in the crawl. I was told to run 2 12 inch flex 25 feet to #2 distribution boxes and run 6 of the 6 inch supplies off of each of the distibution boxes and run the remaining 3 straight off the supply plenum. I'm curious if both the 12 inch flex can carry those 6 runs coming off the distribution boxes. I have already suggested we run 14 to the distribution boxes but I was told 12 inch flex would be fine. I want to know what you would do in this situation??????

Run it in hard pipe , that's all I have ever been taught.
I just got done rippping out 200' of flex in a crawl , half the runs were not getting enough airflow and the other half you could fart harder than they were blowing.
Of course they were all coming off of the plenum though.
I am curious to know how the system would work if you ran
the flex to distribution boxes? Let us know how it turns out!

Originally posted by blu70devil I'm in the middle of installing a Trane 3 ton heat pump sytem. There are 15 6 inch supplies in the crawl. I was told to run 2 12 inch flex 25 feet to #2 distribution boxes and run 6 of the 6 inch supplies off of each of the distibution boxes and run the remaining 3 straight off the supply plenum. I'm curious if both the 12 inch flex can carry those 6 runs coming off the distribution boxes. I have already suggested we run 14 to the distribution boxes but I was told 12 inch flex would be fine. I want to know what you would do in this situation??????

You will liklely need balancing dambers at each takeoff,as it's not likely that every supply would be 6" flex.

will you be there for start-up??

The 12" flexes are most likely large enough to handle the systems air flow,I just doubt it will be the correct cfm in each room.

I finished the job today and the airflow seemed to be just fine. We replaced a 3 ton Trane heat pump for another 3 ton Trane heat pump. The customer said that the airflow was actually better than before. Flex may not be the best thing for a crawl space but thats the only option I have at my company and it seems to be the thing to do here in NC. Overall the job looked great and the customer was very happy with our install.In the end you cant ask for much more than that. Thanks for all the input guys.